The present invention relates to a frit-sealing apparatus for a cathode-ray tube, which is used when a panel and a funnel constituting the cathode-ray tube are joined by fusing frit glass.
FIG. 13 is a schematic illustration of the configuration of a conventional frit-sealing apparatus for a cathode-ray tube, with parts partially broken away. FIG. 14 is a sectional view taken along the line S.sub.14 --S.sub.14 of FIG. 13.
As shown in FIG. 13 and FIG. 14, when the conventional frit-sealing apparatus for a cathode-ray tube is used to join the panel and the funnel 2 by fusing frit glass in a frit seal furnace (not shown), the nozzle portion 10 for letting air flow back from the cathode-ray tube is inserted into the funnel 2 (the inserted position is indicated by the solid line in FIG. 13) and then withdrawn (the withdrawn position is indicated by the broken line in FIG. 13) in such a manner that the nozzle 10 does not touch the neck portion 2a of the funnel 2.
The nozzle portion 10 is inserted and withdrawn by moving the guide block 31 supporting the nozzle portion 10 along the guide rod 32 in the directions A. The guide block 31 and the guide rod 32 each have a keyway. The key member 33 is fitted to the keyway formed on the guide block 31. The key member 33 is also fitted to the keyway formed on the guide rod 32 so as to slide along the keyway. The key member 33 has a function to prevent the guide block 31 from rotating on the guide rod 32.
However, while the conventional frit-sealing apparatus for a cathode-ray tube is traveling in the heated frit seal furnace, the guide rod 32 may be heat-distorted to warp or the guide rod 32 or key member 33 may be expanded by heat to make the guide rod 32 and the guide block 31 jammed. This makes it impossible to lower the guide block 31. Because the nozzle portion 10 can not be withdrawn, the cathode-ray tube can not be removed.
Dust originating from the chain of a carrying mesh belt in the frit seal furnace or the like or soot formed by incomplete combustion of a radiant tube or the like may be deposited on the keyway of the guide rod 32, making the key member 33 jammed in the keyway of the guide rod 32. This makes it impossible to lower the guide block 31. Because the nozzle portion 10 cannot be withdrawn, the cathode-ray tube can not be removed.
If a cathode-ray tube cannot be removed while a plurality of cathode-ray tubes are conveyed in order on the carrying mesh belt, the mesh belt stops, leaving some cathode-ray tubes overheated for a long time in the frit seal furnace. This results in thermal plastic deformation of the panel, the funnel and the mask frame for color selection, significantly degrading the product quality of the cathode-ray tube.